Gliese 667
Gliese 667 (142 G. Scorpii) is a triple-star system in the constellation of Scorpius, all of whose components have masses smaller than the Sun. The system lies at a distance of about 6.8 pc (22.1 ly) from Earth. There is a 12th magnitude star close to the other three, but it is not gravitationally bound to the system. To the naked eye, the system appears to be a single faint star of magnitude 5.89. The system has a relatively high proper motion, exceeding 1 second of arc per year. Trinary star system The two brightest components of this system, GJ 667 A and GJ 667 B, are orbiting each other at an average angular separation of 1.81 arcseconds with a high eccentricity of 0.58. At the estimated distance of this system, this is equivalent to a physical separation of about 12.6 AU, or nearly 13 times the separation of the Earth from the Sun. Their eccentric orbit brings the pair as close as about 5 AU to each other, or as distant as 20 AU, corresponding to an eccentricity of 0.6.Based on a calculated eccentricity value of \scriptstyle e= . This orbit takes approximately 42.15 years to complete and the orbital plane is inclined at an angle of 128° to the line of sight from the Earth. The third component, GJ 667 C, orbits the GJ 667 AB pair at an angular separation of about 30", which equates to a minimum separation of 230 AU. Gliese 667 A The largest component of this system, Gliese 667 A (GJ 667 A), is a K-type main-sequence star of stellar classification K3V. It has about 73% of the mass of the Sun and 76% of the Sun's radius, but is radiating only around 12-13% of the luminosity of the Sun. The concentration of elements other than hydrogen and helium, what astronomers term the star's metallicity, is much lower than in the Sun with a relative abundance of around 26% solar. The apparent visual magnitude of this star is 6.29, which, at the star's estimated distance, gives an absolute magnitude of around 7.07 (assuming negligible extinction from interstellar matter). Gliese 667 B Like the primary, the secondary component Gliese 667 B (GJ 667 B) is a K-type main-sequence star, although it has a slightly later stellar classification of K5V. This component has a mass of about 69% of the Sun, or 95% of the primary's mass, and it is radiating about 5% of the Sun's visual luminosity. The secondary's apparent magnitude is 7.24, giving it an absolute magnitude of around 8.02. Gliese 667 C Gliese 667 C is the smallest stellar component of this system, with only around 31% of the mass of the Sun and 42% of the Sun's radius. It is a red dwarf with a stellar classification of M1.5. This star is radiating only 1.4% of the Sun's luminosity from its outer atmosphere at a relatively cool effective temperature of 3,700 K. This temperature is what gives it the red-hued glow that is a characteristic of M-type stars. The apparent magnitude of this component is 10.25, giving it an absolute magnitude of about 11.03. It is known to have a system of two planets: claims have been made for up to seven but these may be in error due to failure to account for correlated noise in the radial velocity data. From the surface of Gliese 667 Cc, the second confirmed planet out that orbits along the middle of the habitable zone, Gliese 667 C would have an angular diameter of 1.24 degrees and would appear to be 2.3 times \begin{smallmatrix}\frac {h} ={\left( \frac _{\rm eff}} \right)^2} *\frac{\sqrt{L}} {a}\end{smallmatrix} . where \begin{smallmatrix}{h}\end{smallmatrix} is the apparent visual diameter of the star from the surface of the planet in orbit (GJ667Cc in this case), \begin{smallmatrix} \end{smallmatrix} is the apparent visual diameter of the Sun (sol) from the surface of Earth, \begin{smallmatrix} _{\rm eff}\end{smallmatrix} is the effective temperature of the Sun (sol), \begin{smallmatrix} \end{smallmatrix} the effective temperature of the star, \begin{smallmatrix}{L}\end{smallmatrix} is the luminosity of the star as a fraction of the sun's luminosity and \begin{smallmatrix}{a}\end{smallmatrix} is the distance of the planet from the star in AU. the visual diameter of our Sun, as it appears from the surface of the Earth. Gliese 667 C would have a visual area 5.4 times greater than that of the Sun but would still only occupy 0.003 percent of Gliese 667 Cc's sky sphere or 0.006 percent of the visible sky when directly overhead. Note: see VizieR catalogue J/A+A/367/521. }} References Category:Astronomy Category:Trinary star systems